It seems a good part of Mozilla's problems keeping users are actually being caused by Google. Besides the constant incompatibilities introduced by Google there's this:

This is Firefox's CPU utilization when just looking at Google's search page in a private window since Google turned on AI by default. My laptop literally gets too hot to be used on my lap. The exact same search on Chrome takes less than 2% CPU. (Yes, I know about Duckduckgo.)
Recently disabling native AI features in Firefox significantly reduced CPU use, but a couple of days ago it shot up again only when on Google's search page.